Fan system



H. F. HAGEN June 6, 1939.

FAN SYSTEM Filed Aug. l2, 1936 ELEcrmc AN T VOLTAGE j. 11g 3. To FieldBA1-Miura To Armo'fnre To Fichi To Eled'r-c In vegqhf TV- /AfeoLo F".HAGEN 6o Lg J. C7 48 d/orneg Patent-ed June 6, 1939 UNITEDv STATESPATENT OFFICE FAN SYSTEM Mass.

Application August l2. 1936, Serial No. 95,675

11 Claims.

This invention relates to fan systems and relates more particularly to afan system providing forced and induced draft in balanced relationship.

Steam power plants use forced draft fans for supplying air underpressure to the burners for combustion, and use separate induced draftfans usually spaced a substantial distance from the forced draft fansfor drawing the furnace gases through the heat exchangers and fordischarging the exhaust gases from the stack. 'Ihe forced draft fanusually takes care of the air resistance of a steam plant as far as thetop of the fuel bed. The induced draft fan usually takes care of the l5resistance from the fire box through the boiler and economizer. In atypical steam plant for a given plant load and corresponding air volume,a pressure corresponding to 4 inches of water may be provided by theforced draft fan and a static suction corresponding to 2 inches of watermay be provided by the induced draft fan. The pressure drop or pressuredifferential through the plant in such a case is 6 inches of water ofwhich 4 inches is provided by the forced draft and 2 inches is providedby the induced draft fan.

For different plant loads, different quantities of fuel are burned anddifferent volumes of air are required for efficient combustion. Forsupplying different air volumes into the combustion chamber, differentpressures are required from the forced draft fan, and different staticsuctions are required from the induced draft fan for drawing the airwith the products of combustion from the chamber. The characteristics ofa steam plant are such however, that the proportions of the pressuredifferential required from the two fans for different loads and airvolumes, are not constant. As the plant load decreases and the volume ofair required for efficient combustion is conformably decreased, theproportion of the pressure differential required from the forced draftfan increases and the proportion required from the induced draft fandecreases. This is due to adjustment of fuel burning and associatedapparatus at reduced loads which result in greater forced draftrequirements.

According to this invention, a forced draft fan and its associatedinduced draft fan are mounted on a single shaft and both are driven by asingle motor. Among the advantages of this arrangement are: less spaceis required; smaller and cheaper foundations may be used; two bearings,two pedestals and one coupling may be elimi- 55 nated; the fluearrangement may be simplified,

and the first cost and cost of maintenance are less.

It is desired to vary the volumes of air supplied to the plantconformably with changes in the load on the plant by adjusting thepressures supplied by the forced draft fan. This may be accomplished,for example, by varying the speed of the single motor driving both fansto provide the pressure required from the forced draft fan. But, asexplained in the foregoing, the proportions of the pressure differentialrequired from the forced draft fan and from the induced draft fan forovercoming the plant resistance, vary with the total air volume. For agiven air volume which may be, for example, the maximum air volume tocorrespond to the maximum plant load, the fans may be designed toexactly handle their duties without adjustment of either. But, for loadsbelow the maximum, the proportion of the pressure differential requiredfrom the forced draft fan is reduced a smaller percentage than thatrequired from the induced draft fan, with the result that if the fansare operated so that the pressures required from the forced draft fanare supplied for air volumes below the maximum,

the induced draft fan will operate to produce too great a suction in thecombustion chamber.

In one embodiment of this invention, a forced draft fan and a matchedinduced draft fan are rotated by a single motor, and the volumes of airprovided by operation of the fans are varied conformably with the loadon the steam plant by adjusting the speed 0f the motor driving bothfans, in accordance with the pressure requirements from the forced draftfan. As a result of the difference in the requirements from the two fansat reduced loads, when the total volume is decreased in accordance withthe requirements from the forced draft fan, the induced draft fan tendsto create too great a suction, and to cornpensate for this, adjustablespin inducing vanes are provided in the inlet of the induced draft fan,which vanes are adjusted to decrease the effect of the induced draft fanupon the gases it handles so as to maintain the negative pressure orfurnace draft in the combustion chamber within the desired limits.

An object of the invention is to mount the wheels of a forced draft andof an induced draft fan on a single shaft.

Another object of the invention is to compensate for the difference inthe requirements by a steam plant at different loads, from forced andinduced draft fans driven by a single motor.

Another object of the invention is to drive in a steam plant, similarlyrated forced and induced draft fans at the same speed; to adjust thetotal volume of air provided by the operation of the fans, in accordancewith the plant requirements from the forced draft fan at differentloads, and to independently adjust the effect of the induced draft fanupon the gases it handles to compensate for the difference in therequirements by the plant from the forced draft and induced draft fansatdifferent loads.

Other objects of the invention will be apparent from the followingdescription taken together with the drawing.

The invention will now be described with reference to the drawing, ofwhich:

Fig. 1 is a diagrammatic view of a fan system with controls embodyingthis invention;

Fig. 2 is a chart illustrating the requirements of the steam plant ofFig. 1 from the forced draft fan and from the induced draft fan atdifferent plant loads, and

Fig. 3 isa circuit scheme illustrating relay switching for reversing thevane adjusting motor of the induced draft fan.

Referring first to the chart of Fig. 2, the abscissa entitled Plantloads represents the loads under which it is expected the steam plant ofFig. l will be operated. 'I'he ordinate entitled Pressure differentialsrepresents the pressure differentials required by the plant from the twofans at different plant loads. 'Ihe curve entitled Total from both fansrepresents the pressure differentials required by the plant from bothfans at different plant loads. The curve entitled Forced draft fanrepresents the pressure differentials required by the plant from theforced draft fan at different plant loads. The curve entitled "Induceddraft fan represents the pressure differentials required by the plantfrom the induced draft fan at different plant loads. For the purpose ofillustration, at the maximum plant load, the forced draft fan is shownto provide 4 inches and the induced draft fan to provide 2 inches, of atotal of 6 inches of pressure differential required for providing thevolume of air required to efciently burn the fuel supplied to the plant.

Under lighter loads, less fuel is burned, reduced volumes of air andlower pressure diiferentials are required. But, for reduced loads theforced and induced draft fans do not provide the same proportions of thepressure differen-y tials through the plant that they do at maximumplant load. The chart of Fig. 2 shows that for loads below the maximum,the forced draft fan is required to provide greater proportions and theinduced draft fan is required to provide less proportions of thepressure differentials. If the total volume is adjusted in accordancewith forced draft requirements as is preferred, without independentadjustment of the induced draft fan, the induced draft fan would beoperated to produce too great a suction in the combustion chamber. Thisinvention provides broadly for adjusting the air volume supplied to theplant, in accordance with the requirements by the plant and foradjusting the volume handledby one of the fans for compensating for thedifference in the proportions of the pressure differential required bythe plant from the two fans at different loads, and providesspecifically for adjusting the air volume supplied to the plant, inaccordance with the forced draft requirements at different loads, andfor additionally adjusting the suction of the induced draft fan forcompensating for the reduced duty required from it at the reduced loads.In other Words, this invention provides for causing the performances ofthe two fans to follow the two lower curves of Fig. 2 to overcome theirtendency to follow curves which would be substantially equidistant alongtheir lengths.

In the embodiment illustrated, the changes in plant load cause theforced draft fan to provide the pressure differentials along the curveentitled Forced draft fan for providing variable volumes of air forforced draft. A suction control preferably mounted in the combustionchamber then causes the induced draft fan to provide the pressuredifferentials along the curve entitled Induced draft fan.

The forced draft fan 5, Without inlet vanes, is preferably of thegeneral type disclosed by my Patent No. 1,989,413 with a single inlet.The induced draft fan 6 with inlet vanes 65 is preferably similar to theone disclosed by my Patent No. 1,846,863 with the exception that in thepresent case, a fan with single inlet is illustrated. The two fans 5 andhave their wheels mounted for rotation upon the same shaft 'I, which isrotated by the variable speed electric 1notor.3.

Mounted within the inlet chamber 9 of the induced draft fan 6 are theadjustable vanes 65, the function, arrangement and adjustment of which,are identical with the disclosure of my said Patent No. 1,846,863, andso will not be described in detail here. It is believed suflicient tostate that the cranks and links etc., indicated generally by l0 areadjusted by the rotation of the gear Il, corresponding to the gearindicated by 48 in my said patent. The gear II is in turn rotated by thegear I2 mounted on the same shaft as the gear I3 which is rotated by thegear I5, mounted on the shaft of the motor I6, through the intermediaryof the chain or belt I4. Rotation of the armature of the motor I6 in onedirection adjusts the vanes 65 towards their full open position androtation of the armature in the .other direction adjusts the vanestowards their closed position. The operation and direction of rotationofthe motor I6 are controlled by the relays I'I and I8 which in turn arecontrolled by the furnace pressure controller indicated generally by I9,as will be explained in more detail in the following.

The header 20 of the steam plant indicated generally by 2I is connectedby the pipe 22 to the pressure chamber 23 Which'acts upon increases inpressure to move the lever arm 24 against the force of the weights 25and spring 26, upwardly to cause its contact 21 to adjust the value ofthe resistance 28 in the circuit including the wire 29, the threesolenoid coils 30 of the furnace pressure controller I9, the wire 3I,the armature 32 of the galvanometer indicated generally by 36, the wire33, the constant voltage source 34 and the wire 35.

A diaphragm of the chamber 23 raises and lowers the lever 24 inaccordance with changes in the steam pressure in the header 20, whichare a measure of the boiler load. As the load decreases and the pressureincreases, more of the resistance 28 is placed in the above describedcircuit causing a decreased current to flow through the solenoids 30 andthe coil 32 of the galvanometer 36.

This causes the coil 32 to adjust the Contact arm 31 to increase thevolume of the resistor 33 included in the circuit including the arm 31,the resistor 38, the wires 39, the motor 8 and the electric source 40.This causes the motor 3 to operate at a lower speed so as to drive thefans 6 and 6 atreduced speeds.

'I'he furnace pressure controller I9 is preferably similar to thatdisclosed in U. S. Patent No. 1,870,984 to Edward S. Bristol, andillustrated in detail by Figs. 2 and 3 thereof. As shown by Fig. lhereof, the pivoted lever 4I has mounted upon an upright extension, themovable magnetic coil 36a. 'I'he lever 4I has mounted at one end on itsunderside the bell 42, the interior of which communicates through thepipe 43 with the combustion chamber of the boiler. Air, at atmosphericpressure is introduced through the pipe 44 to the exterior of the bell.As explained in said patent to Bristol, the position of the movable coil30a will depend upon the strength of current flow through the coils andupon the difference in pressure between the upper and lower sides of thelever 4I. The upper side of the lever is exposed through the pipe 44 toatmospheric pressure which may be assumed to be constant so that theconflicting forces acting to unbalance the lever 4I are the suctions inthe bell 42 caused by the furnace draft, and the current flow throughthe coils caused by changes in plant load. The lever 4I carries thecontact 45, which when the forces exerted by the bell 42 and thesolenoids 30 and 30a are balanced, is midway between the contacts 46 and41. When the forces are unbalanced, the contacts carried by the arm 45will contact with one or the other of the contacts 46 and 41, causingone or the other of the relays I1 and I8 to become energized to causethe motor I6 to adjust the inlet vanes of the induced draft fan 6 torestore the balanced condition between furnace draft and load byadjusting the suction in the combustion chamber.

The current ow through the solenoid coils 30 and 30a varies with theboiler load and it is desired to adjust the air volume through thefurnace accordingly. Too great an increase in the furnace vacuum causedby too great a suction being applied by the induced draft fan 6, causesthe force exerted by the bell 42 to overcome the opposing force causedby the current flow through the solenoids 30 and 38a, and the lever 4Itilts to the right (facing the drawing) causing the circuit includingthe contact 46, the contact on the arm 45, the wire 48, the solenoid ofthe relay I8, the electric source 49 and the wire 50 to be completedcausing thefsolenoid of the relay I 8 to close circuits to connect thearmature and eld of the motor I6 together and to the current source 49to cause the motor to rotate in a direction to adjust the vanes in theinlet chamber 9 of the induced draft fan 6 towards closed position. Themotor will rotate until the vanes are adjusted to cause the properdecreased vacuum in the combustion chamber.

Too small a suction in the combustion chamber results in the forcecaused by the current iiow through the solenoids 30 being greater thanthe force exerted by the bell 42 so that the lever 4I tilts to the leftcausing the circuit including the contact 41, the wire I, the relay I1,the electric source 49, the wire 50 and the contact 45 to be closedcausing the relay I1 to become energized and the relay I8 to becomedeenergized. The relay I1 then closes contacts as shown by Fig. 3,connecting the armature and field of the motor I6 to the source I4 butin reverse relation to each other so that the motor I6 rotates inreversed direction to adjust the vanes in the inlet chamber 9 of theinduced draft fan 6 towards their open position. The motor will againcontinue to adjust the vanes until the proper vacuum is established inthe combustion chamber.

The motor control mechanism comprising the constant voltage source 34,the chamber- 23, lever 24 and resistance 28, as well as the furnacepressure controller I9 may be of the well known type manufactured by theLeeds & Northrup gompany, and described in their Bulletin No.

While, one embodiment of the invention has been described for thepurpose of illustration, it should be understood that the invention isnot limited to the exact arrangement described, since many departureswill suggest themselves to those skilled in the art, after having hadaccess to this disclosure.

What is claimed is:

1. A steam plant comprising in combination, a combustion chamber, 4aforced draft fan for forcing air into said chamber, a matched induceddraft fan for drawing the exhaust gases from said chamber, a singleshaft supporting the wheels of both of said fans, a motor for rotatingsaid shaft, means for adjusting the speed of said motor in accordancewith the load on said plant, spin inducing vanes in the inlet to saidinduced draft fan, and means for adjusting said vanes to vary thesuction of said induced draft fan in accordance with changes in thesuction in said chamber.

2. A steam plant comprising in combination, a combustion chamber, forceddraft fan for forcing air into said chamber, a matched induced draft fanfor drawing the exhaust gases from said chamber, a single shaftsupporting the wheels of both of said fans, a motor for rotating saidshaft, means responsive to changes in the load on said plant foradjusting the speed of said motor in accordance with the load on saidplant, spin inducing vanes in the inlet to said induced draft fan, andmeans for adjusting said vanes to vary the suction of said induced draftfan in accordance with changes in the suction in said chamber.

3. A steam plant comprising in combination, a combustion chamber, aforced draft fan for forcing air into said chamber, a matched induceddraft fan for drawing the exhaust gases from said chamber, a singleshaft supporting the' wheels of both of said fans, a motor for rotatingsaid shaft, means responsive to changes in the load on said plant foradjusting the speed of said motor in accordance with the load on saidplant, spin inducing vanes in the inlet to said induced draft fan, andmeans responsive to pressure in said chamber for adjusting said vanes tovary the suction of said induced draft fan in accordance with changes inthe suction in said chamber.

4. A fan system for a steam plant adapted to be operated under differentloads and including a boiler having a combustion chamber adapted toreceive air volumes varying conformably with said loads comprising incombination, a forced draft fan for supplying air into said chamber, aninduced draft fan for drawing the air with the products of combustionthrough said plant, the wheels of said fans being mounted on a commonshaft, said fans cooperating to provide variable pressure differentialsfor moving variable volumes of air through said plant, the proportionsof the pressure differentials required by said plant from said induceddraft fan decreasing more than 'the proportions required from saidforced draft fan for decreasing plant loads, means for varying thepressure differential provided by said fans, means responsive to achange in the plant load for actuating said last mentioned means. volumecontrol means in the inlet to one of said fans, and means includingmeans responding conformably to changes in pressure in said chamber foradjusting said volume control means to provide the pressure differentialrequired from said one of saidfans by said plant by said change in load.

5. A fan system for a steam plant adapted to be operated under differentloads and including a boiler having a combustion chamber adapted toreceive air volumes varying conformably with said loads comprising incombination, a forced draft fan for supplying air into said chamber, aninduced draft fan for drawing the air with the products of combustionthrough said plant, the wheels of said fans being mounte on a commonshaft, said fans cooperating to overcome the resistance of said plantfor moving variable volumes of air therethrough, the suctions requiredby said plant from said induced draft fan decreasing more in proportionthan the pressures required from said forced draft fan for decreasingplant loads, means for varying the pressure provided by said forceddraft fan for varying the volume of air supplied into said chamber,means responsive to a change in the plant load for actuating said lastmentioned means, volume control means in the inlet to said induced draftfan, and means including means responding conformably to changes insuction in said chamber for adjusting said volume control means toprovide the suction required from said induced draft fan by said plantby said change in load.

6. A fan system for a steam plant adapted to be operated under differentloads and including a boiler having a combustion chamber adapted tovreceive air volumes varying conformably with said loads comprising incombination, a forced draft fan for supplying air into said chamber, aninduced draft fan for drawing the air with the products of combustionthrough said plant, the.

wheels of said fans being mounted on a common shaft, said fanscooperating to provide variable pressure differentials for movingvariable volumes of air through said plant, the proportions of thepressure differentials required by said plant from said induced draftfan decreasing more than the proportions required from said forced draftfan for reduced plant loads, means for varying the pressure differentialprovided by said fans, means responsiveto a change in the plant load foractuating said last mentioned means, spin inducing vanes in the inlet toone of said fans, and means including means responding conformably tochanges in pressure in said chamber for adjusting said vanes to providethe pressure differential required from said one of said fans by saidplant by said change in load.

'7. A fan system for a steam plant adapted to be operated underdifferent loads and including a boiler having a combustion chamberadapted to receive air volumes varying conformably with said loadscomprising in combination, a forced draft fan for supplying air intosaid chamber, an induced draft fan for drawing the air with the productsof combustion through said plant, the Wheels of said fans being mountedon a common shaft, said fans cooperating to overcome the resistance ofsaid plant for moving variable volurnes of air therethrough, thesuctions required by said plant from said induced draft fan decreasingmore in proportion than the pressures required from said forced draftfan for decreasing plant loads, means for varying the pressure providedby said forced draft fan for varying the volume of air supplied intosaid chamber, means responsive to a change in the plant load foractuating said lastl mentioned means, spin inducing vanes in the inletto said induced draft fan, and means including means respondingconformably to changes in suction in said chamber for adjusting saidvanes to provide the suction required from said induced draft fan bysaid plant by said change in load.

8. A fan system for a steam plant adapted to be operated under differentloads and including a boiler having a combustion chamber adapted toreceive air volumes varying conformably with said loads comprising incombination, a forced draft fan for supplying air into said chamber, aninduced draft fan for drawing the air with the products of combustionthrough said plant, the

' wheels of said fans being mounted on a common shaft, said fanscooperating to provide variable pressure differentials for movingvariable volumes of air through said plant, the proportions of thepressure differentials required by said plant from said induced draftfan decreasing more than the proportions required from said forced draftfan for decreasing plant loads, means for varying the air volumesupplied into said chamber by varying the total pressure differentialprovided by both of said fans to provide the pressure required by saidplant from said forced draft fan, means responsive to a change in theplant load for actuating said last mentioned means, volume control meansin the inlet to said induced draft fan, and means responding conformablyto changes in pressure in said chamber for adjusting said volume controlmeans to provide the pressure differential required from said induceddraft fan by said plant by said change in load.

9. A fan system for a steam plant adapted to be operated under differentloads and including a boiler having a combustion chamber adapted toreceive air volumes varying conformably with said loads comprising incombination, a forced draft fan for supplying air into said chamber, aninduced draft fan for drawing the air with the products of combustionthrough said plant, the wheels of said fans being mounted on a commonshaft, said fans cooperating to provide variable pressure differentialsfor moving variable volumes of air through said plant, the proportionsof the pressure differentials required by said plant from said induceddraft fan decreasing more than the proportions required from said forceddraft fan for reduced plant loads, means for varying the air volumesupplied into said chamber by varying the total pressure differentialprovided by both of said fans to provide the pressure differentialrequired by said plant from said forced draft fan, means responsive to achange in the plant load for actuating said last mentioned means, spininducing vanes in the inlet to said induced draft fan, and meansincluding means responding conformably to changes in pressure in saidchamber for adjusting said vanes to provide the pressure differentialrequired from said induced draft fan by said plant by said change inload.

10. A fan system for a steam plant having a combustion chamber,comprising a forced draft fan for forcing air into said chamber, aninduced fill draft fan for drawing the air with theproducts ofcombustion from said chamber, the wheels of said fans being driven bycommon means, means responsive to changes in the load upon said plantfor varying the pressures provided by said forced draft fan for varyingthe volumes of air supplied to said chamber, volume control means in theinlet vof said induced draft fan, and means including means respondingconformably to suction changes in said chamber for adjusting said volumecontrol means for varying the suction of said induced draft fanconformably with changes in the suction in said chamber.

11. A fan system for asteam plant having a combustion chamber,comprising a forced draft fan for forcing air into said chamber, aninduced draft fan for drawing the air with the products of combustionfrom said chamber, the wheels of said fans being driven by common means,means responsive to changes in the load upon said plant for varying thepressures provided by said forced draft fan for varying the volumes ofair supplied to said chamber, spin inducing vanes in the inlet of saidinduced draft fan, and means including means responding conformably tosuction changes in said chamber for adjusting said spin inducing vanesfor varying the suction of said induced draft fan conformabLv withchanges in the suction in said chamber HAROLD F. HAGIN.

